Capsule OEM Raw Materials: Shell Types, Fill Properties and Glidant Selection Explained
In capsule contract manufacturing, raw materials are the step brands most often overlook. Attention goes to the active ingredient, while two things that actually decide whether a batch succeeds get far less scrutiny: whether the shell is the right one, and whether the fill will run consistently on the machine. Most volume-scale problems we see on line - incomplete locking, leakage, out-of-specification disintegration, shells turning brittle in storage - trace back to material selection or incoming inspection. This guide follows the sequence of shell, fill, glidant, then acceptance, for capsule OEM projects.
1. Choosing a shell: gelatin, HPMC or pullulan
Gelatin remains the lowest-cost and most widely available option. It gives good clarity, fast disintegration and broad filling compatibility, but it has two hard limits. It is animal-derived, which rules it out for vegetarian positioning and some religious dietary requirements. And its moisture content makes it sensitive to storage: in dry conditions shells lose water and become brittle, while in humid conditions they soften and block.
HPMC shells are the mainstream plant-based alternative. They carry low moisture, suit hygroscopic fills and formulations containing aldehydes, and support vegetarian claims - but the unit cost is clearly higher and disintegration behaviour differs from gelatin, so any dissolution or disintegration work must be repeated against the actual shell. Pullulan shells offer excellent clarity and oxygen barrier at a higher price, typically reserved for premium or natural-positioned lines. Judge in this order: fill characteristics, then target consumer and positioning, then budget - not the reverse.
2. Which shell specifications matter
For gelatin shells, bloom strength is the headline figure, typically between 180 and 240 Bloom. Higher bloom gives better mechanical strength but slightly slower dissolution. Viscosity and moisture come next; moisture is usually held between 13 and 16 percent, with lower values risking brittleness and higher ones causing deformation. Disintegration time, heavy metals, sulphur dioxide residue, microbial limits, and consistency of size and lock length across the 000# to 5# range all belong in the specification as well.
One practical point is routinely missed: the shell must be qualified together with the fill, not accepted on the shell supplier's certificate alone. A strongly hygroscopic fill draws moisture out of the shell, and the finished product turns brittle and cracks after a few months on shelf. Formulations containing aldehydes or reducing sugars can cross-link with gelatin and push disintegration time out substantially. Running one accelerated stability cycle at sampling is the cheapest insurance against a wave of returns after launch.
3. Fill material: particle size, bulk density and flow
Hard capsule filling is volumetric, so bulk density governs fill-weight accuracy. When bulk density drifts, the net weight per capsule moves within the same shell size and fill weight variation quickly exceeds pharmacopoeial or internal limits. The control is to write particle size distribution and bulk density into the incoming specification and hold them consistent between batches.
Flow matters just as much. A poorly flowing fill does not pack properly in the dosing disc, producing under-filled or empty capsules. Remedies include granulation, adjusting the particle size distribution, adding a glidant, or moving up a shell size on the equipment side. Note that granulation changes disintegration and dissolution behaviour, so any product carrying a functional claim needs revalidation.
4. Selecting glidants and lubricants
Common glidants include colloidal silicon dioxide, magnesium stearate and talc, all used to reduce inter-particle friction and improve filling flow. Magnesium stearate lubricates well, but excessive levels form a hydrophobic film over the granules and delay disintegration and dissolution; it is usually kept below one percent with mixing time tightly controlled. Colloidal silica improves flow markedly without affecting disintegration, at higher cost and with stricter dust control. Select by running small trials against the actual fill rather than importing a standard formula.
5. Inspection and storage: two recurring failures
The first is shell storage. Shells are highly sensitive to temperature and humidity; store at 15 to 25 degrees Celsius and 35 to 65 percent relative humidity, and reseal any opened cartons on return to stock - leaving them open is the main cause of both brittleness and deformation. The second is batch variation in fill materials. Botanical extracts, probiotics and enzymes vary in activity and moisture by season and lot, so key attributes must be retested on every batch instead of releasing on the supplier's certificate of analysis alone.
Three items belong in the contract: which party buys and owns quality responsibility for materials, the retest list applied to each batch, and how out-of-specification lots are handled and who bears the cost. Settling those up front removes most later disputes.
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About Guangzhou Mesen Health Biotechnology Co., Ltd
Guangzhou Mesen Health Biotechnology Co., Ltd is located in the Huashan Science and Technology Park, Huadu District, Guangzhou. The company has focused on OEM and ODM services for the big health industry for nearly 20 years, operating dedicated research, production, sales and management centres, and maintaining long-term strategic partnerships with well-known Chinese medicine colleges and research institutions. Capabilities span pressed candy, gummies, capsules, solid beverages, herbal teas, plant beverages, protein powders, dietary supplements and enzyme jelly - from formulation development through contract manufacturing. For details on minimum order quantities, sampling lead times and quotations, see our manufacturing advantages and product range, or contact us for a tailored proposal.
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